Electron discharge devices having inner and outer insulating annular projections at the gun end of the device



Dec. 16. 1969 K. H. R. c. KREUCHEN 3,484,642

ELECTRON DISCHARGE DEVICES HAVING INNER AND OUTER INSULATING ANNULAR PROJECTIONS AT THE GUN END OF THE DEVICE Filed Oct. 24. 1966 3 Sheets-Sheet 1 Dec- 6. 969 K H R. c. KREUCHEN ELECTRON DISCHARGE DEVI 0E5 HAVING INNER AND OUTER INSULATING ANNULAR PROJECTIONS AT THE GUN END OF THE DEVICE Filed Oct. 24. 1966 3 Sheets-Sheet 2 H I I -17 23 t 51 FIGS Dec. 16. 1969 K. H. R. c. KREU CHEN 3,484,642

ELECTRON DISCHARGE DEVICES HAVING INNER AND OUTER INSULATING ANNULAR PROJECTIONS AT THE GUN END OF THE DEVICE Filed Oct. 24. 1966 3 Sheets-Sheet 3 91 9o H54 s1 Q 75 74 87 7872 I n 73 United States Patent ELECTRON DISCHARGE DEVICES HAVING IN- NER AND OUTER INSULATING ANNULAR PRO- JECTIONS AT THE GUN END OF THE DEVICE Karl Heinz Robert Christian Kreuchen, Heston, England, assignor to Electric & Musical Industries Limited,

Hayes, England, a company of Great Britain Filed Oct. 24, 1966, Ser. No. 588,777 Claims priority, application Great Britain, Nov. 3, 1965,

46,597/65; Mar. 18, 1966, 11,939/66 Int. Cl. H01j l/88, 19/42 US. Cl. 313-257 Claims ABSTRACT OF THE DISCLOSURE The invention relates to the construction of a gun for an electron discharge device such as a klystron. The gun comprises at least two electrodes which are mounted on a ceramic base member which forms part of the envelope of the device, being sealed to another conducting part of the envelope. On its inner surface the base member is provided with three annular projections and the cathode of the gun has a flange which is seated in the recess formed within the innermost projection and the modulator electrode has a flange which is seated in the trough between the two outer projections. These electrodes are accurately located both by contact of the flanges with the base surface of the ceramic member and by contact of the edges of the flanges with the projections. The projections also serve to increase the leakage path from one electrode to the other. Further projections are provided on the outer surface of the ceramic member to separate the terminal contacts. In an alternative construction the modulator electrode is seated on top of a projection, instead of in the trough between two projections.

This invention relates to electron discharge devices and it relates especially although not exclusively to klystrons.

In a klystron, the electrons from the cathode are focused to form a beam which passes through successive cavities before being collected by a collecting electrode.

The focussing means have usually been electromagnet, but such means render the klystron heavy and bulky, and it has therefore been proposed to substitute electrostatic focussing for electromagnetic focussing. This proposal has however encountered problems of insulation having regard to the high potential differences required between electrodes to achieve electrostatic focussing. The insulation problem is for example encountered in mounting focussing electrodes accurately in position close to but insulated from the walls of the cavities, a large potential difference being required between the focussing electrode and the cavity wall. It has also been encountered in the case of the lead to such a focussing electrode. This lead may pass from the exterior through a metal part of the envelope maintained at the same potential as the cavity walls, and therefore it has also to be insulated.

The construction of the gun may also give rise to difliculty. For example in one gun construction, the cathode and cathode screen, and the modulator electrode are mounted with accuracy relative to one another and relative to a metal part of the envelope and are required to be well insulated from each other.

It has been found that conducting particles are liable to be deposited on the surface of insulators within the envelope of the klystron causing leakage across the insulators, such deposition occurring especially during the degassing baking operation which is a final stage in the manufacture of the tube. It is also found that leakage is "ice liable to occur on insulating surfaces at the exterior of the klystron.

Similar problems may be encountered in other electron discharge devices. An object of the invention is to reduce the problem of insulation encountered in such a device in one or more of the forms enumerated in the preceding paragraphs.

A further object of the present invention is to provide an electron discharge device having an improved electron gun construction in which the location and mutual insulation of electrodes of the gun is facilitated.

A further object of the present invention is to provide an electron discharge device having an improved electron gun construction in which the danger is reduced of electrical leakage among the external terminals for the gun electrodes and from these terminals to other conductive parts of the device.

According to one feature of the present invention there is provided an electron discharge device provided with an electron gun within the envelope thereof, part of said envelope comprising an insulating member to which at least two electrodes of said gun are attached, said member having projections including at least two which are contacted respectively by said electrodes to locate said electrodes, said projections forming a trough between said electrodes whereby the leakage path over the surface of said member from one of said electrodes to the other is longer than the separation of said electrodes.

According to another feature of the present invention there is provided an electron discharge device provided with an electron gun within the envelope thereof, part of said envelope comprising an insulating base member sealed to a cylindrical metal part of said envelope, at least two electrodes of said gun attached to said insulating member, terminals at the exterior face of said insulating member and electrically connected through said member to said electrodes, said member having at least two annular projections on its outer surface and one of said terminals being located between said projections and the other of said terminals being located within the recess formed by the inner one of said projections.

In order that the present invention may be clearly understood and readily carried into effect it will now be described with reference to the accompanying drawings of which:

FIGURE 1 illustrates a longitudinal sectional view of a klystron according to one example of the invention,

FIGURE 2 is a sectional view taken. on the line II of FIGURE 1,

FIGURE 3 is a sectional view of a modified stand-01f insulator which may be used in a klystron such as illustrated in FIGURES l and 2,

FIGURE 4 is a sectional view of the construction of the electron gun of the klystron illustrated in FIGURE 1,

FIGURE 5 is a sectional view of an alternative form of electron gun which may be used in devices according to the invention.

Referring to FIGURE 1, the klystron which is illustrated comprises an electron gun 1 including a thermionic cathode, four resonant cavities 2, 3, 4 and 5 and a collector electrode 6, arranged in that order along the axis of the klystron. Each of the cavities is formed by two transverse copper walls and by part of the copper envelope of the klystron, the transverse walls being denoted by the references 7 and 8 in the case of each cavity and the copper envelope of the klystron being denoted by the reference 9. The walls 7 and 8 are formed with drift tubes 10 and 11 in known manner, having central apertures which are co-axial. All the cavities have plungers 12 which can be moved radially within the cavities for the purpose of tuning. The cavity 2 is the input cavity and high frequency signals can be fed to this cavity by way of a coupling loop 13. The cavity 5, on the other hand, is the output cavity and is coupled to an output waveguide 14 through a dielectric window 15.

To enable the electrons from the source 1 to be focussed so as to form a concentrated axial beam which passes through the cavities 2, 3, 4 and 5 and is finally collected by the collector electrode 6, electrostatic focussing electrodes 16, 17 and 18 are provided between each pair of cavities. When the klystron is operational, a high potential is maintained on the electrodes 16, 17 and 18 relative to the walls 7 and 8 of the cavities and to the envelope 9, and the electrodes 16, 17 and 18 co-act with the apertured walls 7 and 8 to form converging electrostatic lenses. Each of the electrodes 16, 17 and 18 is at a fixed distance from the respective walls 7 and 8 of the two adjacent cavities, and the mounting is achieved, in the case of each focussing electrode, by means of a ceramic insulator 19. Each focussing electrode and insulator is of the same construction, the electrode 17 being in the form of a planar member having a central aperture for passage of the beams and being located in a central aperture in a corresponding insulator 19. Each electrode 17 is secured in position by lips 21 and 22 on the electrode and tongues 23 on the insulator, as described in United States application Ser. No. 588,810 filed by Kreuchen et al. on the same day as the present application. The electrode 17 is located so that a tapped radial hole 51 in the electrode is aligned with a radial hole 52 in the insulator 19. The lead passes through the hole 52 and an aligned hole 53 in the metal envelope 9 and terminates in an end cap 54. Between the insulator 19 and the end cap 54, the lead is sheathed by a ceramic sleeve 55, which has an end portion 56 of reduced diameter projecting into the hole 52 in the insulator 19. To insulate the end cap 54 from the metal envelope 9, it is secured to one end of a Stand-Off insulator 57, the other end of which is secured to a flanged metal piece 58 welded to another flanged metal piece 59, the inner end of which is in turn welded to the envelope 9 around the edge of the hole 53. The end cap 54 and the flanged metal piece 58 are each secured to the insulator 57 by a multi-step brazing process such as described in British patent specification No. 891,705.

The insulator 57 is of a fluted cylindrical form, formed on its internal surface with three annular grooves, being as can be seen in FIGURE 2, re-entrant towards the envelope 9. It has been found that this construction of insulator reduces the risk of conducting particles being deposited over the inner surface of the insulator 57 in such a way as to cause electrical leakage from the envelope 9 to the end cap 54.

The mounting insulator 19 for the electrode 17 is a one piece member formed of high grade ceramic and the apertured central part thereof has three limbs 33 each in the form of a zig-zag or meander. The outer end of each limb is enlarged to form a foot 34 which, as can be seen in FIGURE 1, is thicker, measured in the axial direction, than the rest of the insulator 19. Both the circumferential and axially facing surfaces of the feet 34 are accurately ground, after the ceramic insulator has been fired, in relation to the central aperture of the insulator 19 and the tongues 23, and the axial facing surfaces of the feet 34 contact walls 7 and 8 of the adjacent cavities, whilst the circumferential surfaces of the feet contact the inner surface of the envelope 9. In this way, the location of the electrode is accurately determined. Moreover, as will be appreciated from a consideration of FIGURES 1 and 2, there is no direct path on the surface of the insulator 19 from the electrode 17 to either of the adjacent walls 7 and 8, or the envelope 9. Any path on the surface of the insulator 19 is long compared with the shortest distance from a point of contact with the electrode and a point of contact with the conductive surfaces 7, 8 and 9. This feature serves to reduce the risk of the klystron. being rendered inoperatively by reason of the surface of the insulator 4 becoming conductive. Other meander forms for the insulator 19 could produce a similar result to the zig-zag meander illustrated.

The insulator 57 may also have a different form from that illustrated in FIGURE 2 and the grooves may be of different shape, provided that they are re-entrant towards the envelope of the tube. Moreover the number of grooves may differ from that shown, and in the form of insulator which is illustrated in FIGURE 3, the number of the grooves 60 is increased to nine.

Referring now to FIGURE 4 which illustrates the construction of the gun of the klystron illustrated in FIGURE 1, a cup shaped one piece ceramic member 71 which forms one end wall of the envelope, supports a cathode 72 by means of the flange 73. The cathode is heated by means of a heater 74 which is connected to a terminal 75 passing through the ceramic member 71. Surrounding the cathode 72 is a tubular screen electrode 76 having an outwardly directed annular flange for locating it against the base of the member 71. Both the cathode 72 and the shield 76 are provided with apertures through which passes the conductor 78 connecting the heater 74 to the terminal 75. The external part of the terminal 81 is located between the projections 90 and 91 and the external part of the terminal 75 is located in the recess formed by the projection 90. The electron emission from the cathode is controlled by means of a modulator electrode 79 which is provided with a flange 80 abutting against the ceramic member 71, a terminal 81 being provided passing through the ceramic member 71 to enable a potential to be applied to the modulator electrode 79. The parts of the terminals 75 and 81 outside the envelope are formed as ceramic to metal seals into which the bolts of the terminals are screwed. The ceramic member 71 has a flange which is joined to the main wall 9 of the device by means of the annular member 83. Three flanged metal annuli 84, and 86 are provided to form the vacuum seal between the member 71 and the main wall 9, the annulus 84 being attached to the main wall 9, the annulus 86 being attached to the member 71 and the annulus 85 which is welded to the annuli 84 and 86 bridging the gap between 84 and 86. In FIGURE 1 the illustration of the join between the main wall 9 and the ceramic member 71 has been simplified.

The ceramic member 71 is axially symmetrical and has on its inner surface three annular projections 87, 88 and 89 between which two troughs are formed. The inner surface of the inner recess in the member 71 bounded by the projection 87 is accurately machined to provide accurate location of the cathode and the cathode screen by means of the flanges provided thereon which have the same diameter as the inner boundary of the projection 87. The inner surface of the member 71 between the projections 88 and 89 is also accurately machined so as to provide accurate location for the modulator electrode 79 by means of the flange 80 which fits in the trough between the projections 88 and 89. It will be observed that both the cathode 72 and the modulator electrode 79 are accurately located by reason of their flanges being seated on the base surface of the member 71 and by reason of the edges of their flanges being in contact with the projections 87, 88 and 89. The outer surface of the ceramic member 71 is also provided with two annular projections 90 and 91. The projections on the ceramic member 71 serve to increase the electric leakage path over the surface of the member between the electrodes and between terminals connected to the electrodes, as well as providing the location for the electrodes 72, 76 and 79. Moreover, the projection 90 and 91 on the outer surface of the member 71 serve to protect the terminals 75 and 81 from accidental damage. The flange on the member 71 which is sealed to the envelope 9, and the projection 91 also provide a long leakage path from the conducting part of the envelope of the klystron to the terminals 75 and 81.

FIGURE 5 shows an arrangement alternative to that shown in FIGURE 4, which may be used in klystrons generally similar to that shown in FIGURE 1. In the case of FIGURE 5, the flange 80 on the modulator electrode 79 sits on one of the annular projections on the inner surface of the member 71, the location of the modulator electrode being provided by the terminals connected to the electrode, of which one only is shown in FIGURE 5 and bears the reference 81. In other respects the arrangement of FIGURE 5 is similar to that of FIGURE 4 except that the annular member 83 is replaced by the wall 7 formed with the drift tube 10 of the first cavity. There is a vacuum seal from 7 to the main wall 9 of the device and another vacuum seal from 7 to the ceramic member 71.

It will be appreciated that the essential surfaces of the ceramic member 71 may be accurately ground by virtue of its axial symmetry and assuming that the flanges on the cathode shield and modulator electrode are accurately formed by suitable precision operations, the accurate assembly of the gun is a relatively simple matter. Moreover, the gun so produced is sturdy and not easily damaged.

Although the invention has been described herein as applied to a klystron, it is also applicable to other high power tubes such as travelling wave tubes.

What we claim is:

1. An electron discharge device provided with an electron gun within the envelope thereof, part of said envelope comprising an insulating member to which at least two electrodes of said gun are attached, said member having annular projections on the same surface, including at least an inner annular projection and an outer annular projection round said inner annular projection, said two projections being contacted externally respectively by said electrodes to locate said electrodes and said projections forming a trough between said electrodes whereby the leakage path over the surface of said member from one of said electrodes to the other is longer than the separation of said electrodes.

2. An electron discharge device according to claim 1 in which one of said electrodes is in contact with the inner surface of said inner annular projection and the other of said electrodes is in contact with the outer surface of said outer annular projection.

3. An electron discharge device according to claim 1 in which one of said electrodes is in contact with the inner surface of said inner annular projection and the other of said electrodes is in contact with the top surface of said outer annular projection.

4. An electron discharge device according to claim 1 in which each of said two electrodes is flanged, the flanges being seated against the base surface of said member and the edges of the flanges being in contact with the respective annular projections.

5. A device according to claim 1 further comprising focussing means for constraining electrons from said gun to travel as a beam past successive energy interchange means, and means for collecting said electrons.

6. A device according to claim 5 in which said focussing means includes an electrode provided with a lead which passes through a conducting part of said device and is separated from said conducting part by a stand-01f insulator formed with one or more internal grooves which are re-entrant towards the envelope.

7. An electron discharge device provided with an electron gun within the envelope thereof, part of said envelope comprising an insulating member to which at least two electrodes of said gun are attached, said insulating member being formed with at least two spaced annular projections forming a trough between said projections, one of said electrodes of said gun being seated in said trough in contact with said projections, and the other of said electrodes being separated from said first electrode by at least one of said projections.

8. An electron discharge device provided with an electron gun within the envelope thereof, part of said envelope comprising an insulating member having at least three spaced annular projections forming a first trough between first and second of said projections and forming a second trough between second and third of said projections, one electrode of said gun seated in the recess formed by the innermost of said annular projections and in contact with said projection, and a second electrode of said gun seated in the trough formed between and in contact with said two other projections, the other trough being located between said two electrodes.

9. An electron discharge device provided with an electron gun within the envelope thereof, part of said envelope comprising an insulating base member sealed to a cylindrical metal part of said envelope, at least two electrodes of said gun attached to said insulating member, terminals at the exterior face of said insulating member and electrically connected through said member to said electrodes, said member having at least two annular projections on its outer surface and one of said terminals being located between said projections and the other of said terminals being located within the recess formed by the inner one of said projections.

10. An electron discharge device according to claim 9 in which said insulating member forms the base member of said envelope and has a flange sealed to a metal part of said envelope.

References Cited UNITED STATES PATENTS 2,814,751 11/1957 Murdock et al. 313257 X 2,456,861 12/1948 Carter 315-5.34 X 2,604,605 7/1952 Varian 3155.37 X 2,986,672 5/1961 Vaccaro et al. 315-5.34 3,254,259 5/1966 Van der Jagt 313-284 X HERMAN KARL SAALBACH, Primary Examiner PAUL L. GENSLER, Assistant Examiner US. Cl. X.R. 

